Field
This invention relates generally to a diplexed multiple beam integrated antenna system and, more particularly, to a diplexed multiple beam integrated antenna system for a low Earth orbit (LEO) satellite that includes feed horns having a profile that is optimized for both up-link and down-link signals.
Discussion
Recently, there has been a tremendous growth in the use of multiple-beam antenna (MBA) systems for satellite communications, such as direct-broadcast satellites (DBS), personal communications satellites (PCS), military communications satellites, high-speed Internet application satellites, etc. These MBA systems provide coverage to a specific geographical region on the Earth, either contiguously or non-contiguously, using a large number of spot beams that support both down-link (satellite-to-ground) and up-link (ground-to-satellite) frequency bands. The design objectives for MBA systems typically include maximizing a minimum gain over the coverage region, maximizing a pattern roll-off outside the spot-beam area, and minimizing side-lobe radiation in order to maximize frequency reuse. The main advantages of MBA systems over contoured beam payloads include increased spectral utilization achieved through the re-use of frequencies over several spot beams instead of using the whole spectrum on a single contoured beam, increased antenna gain due to a much smaller beam size resulting in higher effective isotropic radiated power (EIRP) on the down-link and higher gain-to-noise temperature (G/T) on the up-link, increased capacity, and smaller ground terminals.
MBA systems typically use either a single-aperture design with complex beam-forming networks, or multiple-aperture designs without beam-forming networks. These types of antennas typically use three-cell, four-cell or seven-cell frequency-reuse schemes in order to increase the effective bandwidth by several fold.
The design of single-aperture multiple-beam antennas has been described in the art using the known “basic-feed concept” and the “enhanced-feed concept.” It has been shown that using overlapping feed clusters in the enhanced-feed concept can achieve good electrical performance through a complex beam-former that requires an element-sharing network and a beam-forming network. Multiple-aperture multiple-beam antennas have the benefits of hardware simplicity and better electrical performance as compared to single-aperture multiple-beam antennas, but at the expense of an increased number of apertures.
The above described MBA systems have been successfully used in the past for geo-synchronous satellites that support personal communications, direct-to-home broadcasts, military communications and mobile communications services. LEO satellite constellations require a large number of satellites arranged in various elliptical orbital planes, where a number of the satellites are placed in each of the orbital planes. The number of the LEO satellites required for global coverage ranges from tens to thousands depending on the altitude of the satellites. Each satellite is required to provide an up-link and down-link signal with the ground and requires a gateway and an inter-satellite link. The cost of the satellite grows with the complexity of the antenna system, where a typical communications link uses two separate antennas, one for the down-link and one for the up-link signal.